Cellen 2

Data visualisation — colour

Gavin Simpson
gavin@anivet.au.dk

Aarhus University

2025-02-20

Learning objectives

At the end of this video you should have a better understanding of

  • how human brains perceive colour

Colour models

  • Red Green Blue — RGB
    • Hexadecimal (base 16)
    • ‘0’–‘9’ with ‘A’–‘F’ for 10-15
    • Encode 256 values of each colour
    • In R "#AA6633"
    • TVs, Digital cameras, etc
  • Cyan Yellow Magenta Black — CYMK
    • Covers a much wider range of colours than RGB
    • Magazines, printing
  • Hue Chroma Luminance — HCL
    • Hue — colour
    • Chroma — how much of the colour
    • Luminance — brightness
    • Designed to reflect human colour perception
  • Hue Saturation Lightness — HSL

Colour palettes

A colour palette is a the colour scheme or selection used to represent data or design on a graph

Want more than a numerical mapping — want perceptually uniform mappings

  • discrete

  • sequential

  • diverging

Discrete palettes

  • Categorical data

  • Easily distinguishable

  • Favour no one colour

  • Vary H, constant C & L

Sequential palettes

  • Continuous data

  • Brightness & intensity of colour vary

  • Vary C & L, constant H

Sequential multi-hue palettes

  • Continuous data

  • Can vary everything if careful

  • Vary H, C & L

Diverging palettes

  • Continuous data where mid-point means something (0)

  • Single hue in each arm

  • C & L are balanced in each arm

  • C goes to 0 at mid-point

Rainbow

#endrainbow

  • Luminance is not linear or even monotonic

  • Colour vision deficiency

#endrainbow

#endrainbow

Colour vision deficiency

Decreased ability to see colour or differences in colour

  • Red-Green CVD is sex-linked
  • Gene carried on X chromosome
  • Blue-Yellow CVD is not; chromosome 7
  • -anomaly vs -anopia